The present invention relates to an apparatus for guiding, treating, or advancing at least one yarn, of the type commonly used in a melt spinning process. In such process, it is known to use apparatus of the type which comprise a delivery roll and a companion roll associated therewith for enabling a repeated looping of the yarn. In this arrangement, the delivery roll is driven, whereas the companion roll may be constructed with or without a drive unit, as is disclosed, for example, in EP 1 001 521 A2.
According to EP 1 001 521 A2, the delivery roll and the companion roll can each be driven by an electric motor, which is a synchronous motor. By means of a controller the electric motors are controlled at a desired frequency for driving the delivery roll and the companion roll at the same circumferential speed. The layout of the drive units is based on the fact that for maintaining a yarn speed as constant as possible, the circumferential speed of the delivery roll and the circumferential speed of the companion roll must be kept constant. In practice, however, even slight inaccuracies in the casing of the delivery roll or in the casing of the companion roll lead to deviations in the casing diameters, which directly effect a change in the circumferential speeds. This effect results in that on the circumference of the companion roll, the yarn is either decelerated or advanced with overfeed. Interactions of this kind, however, lead to an unsteady advance of the yarn, which has a negative effect in particular when a plurality of yarns advance parallel in side-by-side relationship.
It is therefore an object of the invention to provide an apparatus of the initially described type wherein the yarn can be guided on the circumference of the delivery roll and on the circumference of the companion roll at a substantially constant speed.